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Full text of "Alaskan glacier studies of the National Geographic Society in the Yakutat Bay, Prince William Sound and lower Copper River regions"

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854                                ALASKAN GLACIER STUDIES
and in one place, near the •western edge, to 45°.   It is separated from the sea by a cres-centic terminal moraine and an outwash gravel plain.
Lack of Change. The terminus of the Tebenkof Glacier in 1910 (Fig. 52) was not very different from the conditions in 1909 and, so far as information is available, in previous years. Applegate showed the glacier in 1887 in about the same position as in 1909 and 1910. Photographs from sites occupied by Grant in 1909 show no change during the following year on the eastern edge and only a slight retreat at the western margin of the ice front. There are no earlier photographs.
Terminal Moraines. The terminal moraine is close to the glacier and varies considerably in character. The portion near the eastern center (Fig. 52), having a width of from 700 to 1150 feet, has a hummocky inner surface against which the edge of the ice rests. On it are a few pools, but no large kettles. There is a similar small area near the eastern valley wall. The remainder of the terminal moraine forms a striking contrast with this, being a single ridge or series of small parallel ridges less than 100 feet wide, 20 feet or less in height, and extending across the valley with a shape similar to that of the present terminus of the glacier and at a distance of 600 to 800 feet from it.
Between this terminal moraine ridge and the glacier, both east and west of the broader central portion of the moraine, outwash gravel is still being deposited, the gravel deposit on the east containing small pools possibly due to slumping of a small buried portion of the glacier front. As these gravels were still being built up by glacial streams in 1910, it seems probable that other parts of the terminal moraine deposits have been cut away by these streams and buried by their accumulations.
On the eastern side of the moraine, which was barren in most places, were scattered alders up to eight years old in 1910. On the western side, the outer part of the moraine had willows 10 years old and alders of 12 years growth.
This terminal moraine is not continued by lateral moraines at the borders of the glacier, probably because little morainic material was supplied from the bare rock there. There are, however, discontinuous, linear patches of moraine paralleling the ice edge on the eastern side.
Older Terminal Moraine. On the western side of the valley and about 50 feet outside the terminal moraine, was a fragment of an older terminal moraine, contrasting with the inner one in having much moss and many shrubs growing upon its surface. One willow examined was 18 years old. This furnishes the only evidence of two stages in the recent history of Tebenkof Glacier.
Oviwash Plain. The outwash gravel plain, with a length of 2800 to 4500 feet and a width of about a mile, is, in some parts, still being built up by streams. To the northward it is continued into the bay by a mud flat 400 to 700 feet wide at low tide. This plain is 85 to 50 feet above sea level at the ice edge and slopes at the rate of 60 to 65 feet per mile. Some parts of the outwash gravel plain are, however, no longer being built up and have had no streams for over 20 years, as is shown by an extensive growth of willow and alder thickets. Less than half way between the bay and the glacier are several clumps of tall, symmetrical spruce trees, the largest being about 8 feet in diameter and with an estimated age of a century or more. A pair of small hillocks, which appear from a distance to be rock hills, rise up through the alluvial deposits on the eastern edge of the outwash gravel plain; and there is a single, similar hillock on the western side near the valley wall.